Try it out: If you're not already using add-ons, download a few that look interesting and try them out for a while. If your not happy with them, Disable or remove Add-ons will show you how to get rid of them.

What happened to the Status Bar?

Although the Add-on Bar looks similar to the old status bar, it doesn't have any of its features. The status bar at the bottom of the Firefox window has changed in Firefox 4 and some of its features have been moved to other places. See What happened to the Status Bar? for more details.